Using proprietary techniques (patent pending), the investigators propose to develop a spectrophotometric instrument to measure the total hemoglobin concentration of whole blood and the relative concentrations of oxy-, deoxy-, carboxy-, met-, and sulfhemoglobin. The chief strategy is to make Beer's Law apply to whole blood by minimizing the effects of light scattering, to employ matrix math techniques to solve for the 5 hemoglobin concentrations from optical densities measured at five carefully chosen wavelengths. The instrument we envision would have numerous advantages over those now on the market. It would not hemolyze or dilute the blood and would be much less expensive since it would not employ cumbersome plumbing, pumps or hemolyzers. Unlike existing instruments, it would measure sulfhemoglobin, and its other measurements would not be invalid when sulfhemoglobin, and its other measurements would not be invalid when sulfhemoglobin is present. Because of its superior performance, lower maintenance costs, lower price, and ruggedness, it would compete successfully with existing products for a potentially enormous market: every hospital worldwide and many other clinical labs in which blood gases are measured.